The extendible linkage normally used on such a bellows camera comprises a pair of scissor links or lazytongs on opposite sides of its optical axis, e.g. at the top and at the bottom. In my copending application Ser. No. 831,267 of even date, whose disclosure is hereby incorporated by reference into the present application, I have described and claimed a focusing mechanism including a pair of rack-and-pinion transmissions on the camera housing, controlled by a rotatable knob, which coact with the two scissor links throughout a range of operating positions but are decoupled therefrom in an operative position to facilitate a rapid collapsing of the camera. When the control knob is returned to the operating range, i.e. into or past a position corresponding to focusing on infinity, a re-extension of the lens mount automatically recouples the two racks with the respective scissor links.
In such a camera, as well as in others of the same general type, it is desirable to lock the retracted lens mount to the housing in the collapsed state, particularly where a spring force (possibly that of the resilient bellows) urges the lens mount into its extended position. Thus, the camera is ready for use upon unlocking, provided that the control knob has been restored to the operating range from which it was previously displaced for the collapsing of the camera.